001 // Copyright 2006, 2007, 2008, 2009, 2010, 2011 The Apache Software Foundation
002 //
003 // Licensed under the Apache License, Version 2.0 (the "License");
004 // you may not use this file except in compliance with the License.
005 // You may obtain a copy of the License at
006 //
007 // http://www.apache.org/licenses/LICENSE-2.0
008 //
009 // Unless required by applicable law or agreed to in writing, software
010 // distributed under the License is distributed on an "AS IS" BASIS,
011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012 // See the License for the specific language governing permissions and
013 // limitations under the License.
014
015 package org.apache.tapestry5.corelib.components;
016
017 import org.apache.tapestry5.BindingConstants;
018 import org.apache.tapestry5.ComponentResources;
019 import org.apache.tapestry5.Field;
020 import org.apache.tapestry5.MarkupWriter;
021 import org.apache.tapestry5.ValidationDecorator;
022 import org.apache.tapestry5.annotations.Environmental;
023 import org.apache.tapestry5.annotations.HeartbeatDeferred;
024 import org.apache.tapestry5.annotations.Parameter;
025 import org.apache.tapestry5.annotations.SupportsInformalParameters;
026 import org.apache.tapestry5.dom.Element;
027 import org.apache.tapestry5.ioc.annotations.Inject;
028 import org.apache.tapestry5.ioc.internal.util.InternalUtils;
029
030 /**
031 * Generates a <label> element for a particular field.
032 * <p/>
033 * A Label will render its body, if it has one. However, in most cases it will not have a body, and will render its
034 * {@linkplain org.apache.tapestry5.Field#getLabel() field's label} as it's body. Remember, however, that it is the
035 * field label that will be used in any error messages. The Label component allows for client- and server-side
036 * validation error decorations.
037 *
038 * @tapestrydoc
039 */
040 @SupportsInformalParameters
041 public class Label
042 {
043 /**
044 * The for parameter is used to identify the {@link Field} linked to this label (it is named this way because it
045 * results in the for attribute of the label element).
046 */
047 @Parameter(name = "for", required = true, allowNull = false, defaultPrefix = BindingConstants.COMPONENT)
048 private Field field;
049
050 @Environmental
051 private ValidationDecorator decorator;
052
053 @Inject
054 private ComponentResources resources;
055
056 /**
057 * If true, then the body of the label element (in the template) is ignored. This is used when a designer places a
058 * value inside the <label> element for WYSIWYG purposes, but it should be replaced with a different
059 * (probably, localized) value at runtime. The default is false, so a body will be used if present and the field's
060 * label will only be used if the body is empty or blank.
061 */
062 @Parameter
063 private boolean ignoreBody;
064
065 private Element labelElement;
066
067 boolean beginRender(MarkupWriter writer)
068 {
069 decorator.beforeLabel(field);
070
071 labelElement = writer.element("label");
072
073 resources.renderInformalParameters(writer);
074
075 // Since we don't know if the field has rendered yet, we need to defer writing the for and id
076 // attributes until we know the field has rendered (and set its clientId property). That's
077 // exactly what Heartbeat is for.
078
079 updateAttributes();
080
081 return !ignoreBody;
082 }
083
084 @HeartbeatDeferred
085 private void updateAttributes()
086 {
087 String fieldId = field.getClientId();
088
089 labelElement.forceAttributes("for", fieldId);
090
091 decorator.insideLabel(field, labelElement);
092 }
093
094 void afterRender(MarkupWriter writer)
095 {
096 // If the Label element has a body that renders some non-blank output, that takes precedence
097 // over the label string provided by the field.
098
099 boolean bodyIsBlank = InternalUtils.isBlank(labelElement.getChildMarkup());
100
101 if (bodyIsBlank)
102 writer.write(field.getLabel());
103
104 writer.end(); // label
105
106 decorator.afterLabel(field);
107 }
108 }